The invention relates to the field of electromechanical transducers. More particularly, the invention relates to a piezoelectric transducer for a data entry device.
Electromechanical transducers are used for a variety of applications, including data entry applications such as digitizing pen-and-tablet systems. Data entry systems typically include a writing area, such as a tablet or white board, a position indicating pen, and associated electronics for determining the interaction between the position-indicating pen and the writing area. A digital data entry signal is typically derived to represent the relative position of the position-indicating pen and the tablet.
Ultrasound-based electronic tablets and whiteboards are based on either through-the-air transmission (air transmission) or through-the-surface-of-the-board (solid transmission) of ultrasonic pulses. The position of a movable data-entry device on the writing surface is calculated, typically by the geometric intersection of travel times of ultrasonic pulses measured between the data-entry device and a plurality of fixed-location sensor stations, which are located on the periphery of the writing area. Full coverage of a writing area, such as a tablet or a whiteboard, typically requires a minimum of two fixed-location sensors, and one movable sensor for geometric triangulation.
The actual number of required sensors depends on the radiation angle of the ultrasound transmitter or transmitters (the transmission directivity), the strength of the transmitted signal, the acceptance angle of the ultrasound receivers (the reception directivity), and the sensitivity of the receivers to the vibrational frequency of the transmitted pulses.
Many prior art tablets or writing surfaces which use pen shaped data-entry devices are based on touch-panel technologies. Typically, complicated grid layers extend across the surface, and are held apart by tension underneath the writing surface. The location of a data-entry device, such as a data-entry pen, is determined by the location at which the pen presses the grid layers together. Ibid(trademark) whiteboard from Microtouch, of Methuen, Mass., the SmartBoard(trademark) from Microfield Graphics, of Calgary, Alberta, Canada, and pen-based digitizing tablets from Wacom Co, Ltd., of Saitama, Japan are examples of touch-panel technology electronic whiteboards.
A drawback of touch-panel prior art tablets and whiteboards is that the writing surface is an integral component of the system. As the size of the writing area increases, their portability, ease of installation, and product cost become increasingly problematic.
S. Sindeband, and T. Stone, Position Determining Apparatus, U.S. Pat. No. 5,379,269 (Jan. 3, 1995) disclose an apparatus for determining the position of a movable element over a surface of a solid medium. Sindeband et al. describe an electronic whiteboard system which uses ultrasound to determine the position of a pen-shaped stylus on a writing surface. While Sindeband et al. disclose a movable transmitter, the transmitted ultrasonic energy is required to travel through a solid medium. To obtain a consistent signal through a solid medium, therefore, the transmission characteristics of the solid surface must be uniform.
The establishment of a large homogenous writing structure can be difficult and expensive, and precludes the use of the transmitter pen on a generic surface, such as a white board. Standard white boards are not homogenous structures, typically having a common particle board or Masonite(trademark) composite backing, with an applied top surface that typically has non-uniform surface characteristics.
Therefore, an electronic whiteboard based on the principles of operation disclosed by Sindeband et al. would require that a special whiteboard writing surface be included in the product cost. As well, Sindeband et al. disclose a tethered movable stylus, wherein a transmitter is acoustically coupled to the solid medium, which precludes a writing tip within the stylus.
Despite these drawbacks, prior art grid-based tablets and whiteboards typically include data-entry devices which have the look and feel of a pen, and they are designed to be gripped and used like a pen. The user is not required to orient the data-entry device in any special manner.
Ultrasound-based electronic whiteboards that rely on through-the-air transmission of ultrasound pulses, rather than transmission through the solid medium of the whiteboard, offer the opportunity for a product which excludes a dedicated whiteboard writing surface. As an example of such an implementation, an ultrasound transmitter can be located in the movable, pen-style data-entry device. A fixed-position array of ultrasound receivers is located along the periphery of the writing surface. These sensors are used to triangulate the position of the data-entry device on the surface of the whiteboard. The receivers are typically attached directly to a whiteboard, or are mounted to a frame, which is then attached to a whiteboard or other approximately flat writing surface.
Optimally, a sensor for a pen-shaped data-entry device has a transmission directivity that is omni-directional from the writing tip, thus providing cylindrical symmetry to the transmitted signal, which allows the user to hold the device as any pen would be held, without the need to orient a sensor located on the data-entry device toward other receiving sensors located at the periphery of the writing surface.
In the past, most working examples of omnidirectional ultrasonic transmitters were based on spark-gap designs. L. Roberts, xe2x80x9cThe Lincoln Wandxe2x80x9d, MIT Lincoln Lab Report, Lexington Mass., June 1966, and P. De Bruyne, xe2x80x9cCompact Large-Area Graphic Digitizer for Personal Computersxe2x80x9d, Dec. 1986, pp 49-53, IEEE, disclosed examples of spark-gap data-entry devices for electronic whiteboards.
One significant drawback of spark-gap transmitters is the audible, repeated xe2x80x9csnapxe2x80x9d sound associated with the generation of ultrasound pulses. Another significant drawback with spark-gap transmitters is high power consumption, which makes untethered battery-powered operation impractical, since batteries must be changed or recharged on a frequent basis.
As well, spark gap transmitters typically have a transmitter tip that resides on the entire pointing tip of the movable device. The mechanism for producing a spark gap signal has to act as a point source, requiring that the end of the transmitter pen is used as an acoustic horn. This hardware configuration prevents the use of a writing tip, such as a standard writing implement or pen cartridge, from being placed within the device, with a writing tip extending from the pointing tip of the device, as such that a user can write upon a surface, such as a white board, while simultaneously sending a position signal from the pointing tip to external receivers.
R. Herrington and K. Burgess, Wireless Cursor Control System, U.S. Pat. No. 4,654,648 (Mar. 31, 1987) disclose a xe2x80x9cwireless movable steering means which emits acoustic signalsxe2x80x9d. While Herrington et al. disclose a movable transmitter stylus, the spark gap mechanism inherently precludes the use of a writing pen within the pointing tip of the hand-held stylus.
Similarly, A. Whetstone, S. Fine, W. Banks, and S. Phillips, Graphical Data Device, U.S. Pat. No. 3,838,212 (Jan. 3, 1995) disclose a graphical data device employing a stylus moving over an area to be digitized and utilizing a fast rise time sound energy shock, generated by a spark at the location of the stylus and propagated though the air.
R. Davis and J. Howells, Position Determining Apparatus and Transducer Therefor, U.S. Pat. No. 4,012,588 (Mar. 15, 1977) disclose an apparatus for determining the position of a movable element, wherein xe2x80x9ceach receiver comprises a hollow shell of piezoelectric material, which may be cylindrical or spherical in shape, and resilient conductive means coupled across the inner and outer surface of the shellxe2x80x9d. While Davis et al. disclose a cylindrical symmetry for a complicated, stationary, piezoelectric receiver, they fail to disclose the use of a piezoelectric transmitter having cylindrical symmetry within a movable data entry device. In addition, the inner volume of the disclosed cylindrical receiver is filled with a complicated, conductive resilient filling.
S. Mallicoat, Code-Based Electromagnetic-Field-Responsive Graphic Data-Acquisition System, U.S. Pat. No. 5,248,856 (Sep. 28, 1993) discloses an xe2x80x9celectromagnetic-field-responsive, code-based, graphic data acquisition system for tracking the operational status of a mobile write-effective component in relation to a defined writing-surface areaxe2x80x9d. While Mallicoat discloses a pen within the data-acquisition system, the pen includes retro-reflecting regions interspersed with substantially non-retroreflecting regions dispersed circumferentially around the pen, whereby the retro-reflecting regions optically intersect a scanning zone, and reflect light from a scanning light beam source towards a monitoring structure.
M. Biggs, T. O""Ishi, and M. Knighton, Ultrasonic Pen-Type Data Input Device, U.S. Pat. No. 5,308,936 (May 3, 1994) disclose a movable transmitter pointer which simultaneously emits magnetic pulses and ultrasonic pulses. While Biggs et al. disclose an ultrasonic transducer within a movable pointer, the transducer is comprised of a xe2x80x9cpiezo stackxe2x80x9d, which is coupled to a complex aluminum diaphragm and a brass reaction mass, which occupies the entire pointing tip of the movable transmitter pointer. The disclosed stylus therefore has an inherent disadvantage of spark gap pointer designs, in that the hardware occupies a large volume of the pointer, and precludes the use of a writing tip within the pointer.
P. De Bruyne, Apparatus for Determining the Position of a Movable Object, U.S. Pat. No. 4,758,691 (Jul. 19, 1988) discloses an apparatus which contains xe2x80x9ctwo fixed ultrasound transmitters, an ultrasound receiver forming part of a movable object, and a calculatorxe2x80x9d. De Bruyne discloses a movable ultrasound receiver transducer which consists of a cylindrical condenser having an air gap with one solid and one movable electrode. The disclosed copper foil electrode does not cover the whole circumference of the cylindrical condenser, and results in an effective range of about 210 degrees.
I. Gilchrist, Acoustic Digitizing System, U.S. Pat. No. 4,991,148 (Feb. 5, 1991) discloses an acoustic sensing apparatus which contains xe2x80x9can acoustic point source transmission device mounted on an indicator for transmitting a sequence of periodic acoustic oscillationsxe2x80x9d. The disclosed acoustic point source can be configured as a linear stylus, which includes at least a pair of directional acoustic transmitters located away from the pointing tip of the stylus. For two-dimensional position detection, the apparatus employs xe2x80x9cat least three acoustic receivers arranged in a non-linear fashionxe2x80x9d.
M. Stefik and C Heater, Ultrasound Position Input Device, U.S. Pat. No. 4,814,552 (Mar. 21, 1989) discloses an xe2x80x9cinput device, or stylus, for entering hand drawn forms into a computer using a writing instrument, a pressure switch for determining whether the instrument is in contact with the writing surface, an acoustic transmitter for triangulating the position of the stylus on the surface, and a wireless transmitter for transmitting data and timing information to the computer. In operation, the stylus transmits an infrared signal which the system receives immediately, and an ultrasound pulse which two microphones receive after a delay which is a function of the speed of sound and the distance of the stylus from the microphonexe2x80x9d. While Stefik et al. discloses a stylus having a cylindrical enclosure that contains a felt tip marker, and an ultrasonic transducer located near the marker tip, the disclosed transducer is a directional, can-style transmitter, Part No. 40S2 from Murata, Inc., which has a directivity of not more than 120 degrees. The limited directivity requires that the user must consistently orient the stylus towards the fixed-position receivers located at the periphery of the writing surface, such that the receivers are spaced closely enough such that at least two receivers are always within the 120 degree transmission zone for triangulation of the position of the stylus. If the transmitter stylus is positioned close to any receiver, such as occurs when the receivers are located along the periphery of a whiteboard writing surface, the limited directivity requires a large number of receivers.
J. Romein, Acoustic Writing Combination, Comprising a Stylus With a Writing Tablet, U.S. Pat. No. 4,246,439 (Jan. 20, 1981) discloses an acoustic writing combination which contains a stylus which is xe2x80x9cprovided with two ultrasonic sourcesxe2x80x9d which emit pulse-shaped sound signals. The disclosed sound sources are point shaped or circular shaped, which may comprise piezo-electric ceramic rings. While Romein discloses the use of cylindrical piezo-electric rings, the stylus requires two rings to properly locate the pointing tip of the stylus, and does not include a writing tip at the pointing tip of the stylus.
R. Milner, Acoustic Sonic Positioning Device, U.S. Pat. No. 4,862,152 (Aug. 29, 1989) discloses a three-dimensional position control device suitable for controlling computer displays or robot movements, wherein xe2x80x9csignals from an ultrasonic transmitter are received by multiple receiversxe2x80x9d.
R. Garwin, J. Levine, and M. Schappert, Acoustic Contact Sensor for Handwritten Computer Input, U.S. Pat. No. 4,845,684 (Jul. 4, 1989) discloses an acoustic contact sensor for handwritten input, which includes an ultrasonic sending transducer means.
M. Zuta, Ultrasonic Digitizer Pen Having Integrated Ultrasonic Transmitter and Receiver, U.S. Pat. No. 5,239,139 (Aug. 24, 1993) discloses an ultrasonic digitizer pen which includes an ultrasonic transmitter xe2x80x9cto transmit ultrasonic waves through the air, to illuminate a writing surfacexe2x80x9d. While Zuta discloses discrete piezoelectric layers, the transmitted signal cones from each of the segments do not overlap.
It would be advantageous to provide a transmitter adapted to a movable transmitter pen which allows a user to use the transmitter pen as a standard white board pen, the way a pen normally would be used, wherein the user can write upon a writing surface at any incline angle, and without the necessity to orient the transmitter in the pen toward the receivers located along the periphery of the writing surface, while a transmitted signal between the transmitter pen and external receivers simultaneously provides full capture of everything that is written upon the writing surface.
Small, directional ultrasound transducers that could be fitted near the tip of a hand held, pen-style data entry device are manufactured commercially, and include components such as MA40A3, manufactured by Murata Manufacturing Co. Ltd., Kyoto, Japan. These devices house a small, thin disc of piezoelectric ceramic material, and are limited to a transmission angle of between 100 and 120 degrees. In order to achieve a 360-degree ultrasound transmission pattern, a minimum of three to four transducers must be mounted surrounding the tip of the data-entry device. However, each transducer is 1 centimeter in diameter and approximately 1 centimeter in length. Four such devices, when mounted to surround the tip of a pen, must be protected from obstruction by fingers and or other objects that block the ultrasound path between the transmitter and receiver sensors. This may be an impractical, bulky data-entry device.
The disclosed prior art transducers thus provide basic transmission signals for a movable device, but fail to provide a transducer that can transmit an output signal in a radial manner, such as outwardly from the tip of a data entry pen, which can be received by remote receivers along the periphery of a writing area, such as a white board, while providing access for a writing implement. As well, the disclosed prior art transducers fail to provide a transducer which can transmit an output signal to one or more remote receivers when the transmitter and pen are inclined relative to a writing area. Furthermore, the disclosed omnidirectional prior art transducers fail to demonstrate that the power requirement is low enough to enable wireless, battery powered operation of a data entry device, such as a transmitter pen. The development of such a piezoelectric transducer would constitute a major technological advance.
A piezoelectric transducer is provided, in which a piezoelectric cylindrical shell has conductive layers on the outside and inside of the shell, which are adapted to be connected to a signal input source. When the conductive layers are activated by the signal input source, the piezoelectric layer resonates to produce an output signal waveform, typically having a characteristic sound pressure level, from the shell structure. Alternative embodiments include a flat piezoelectric layer with opposing conductive layers, which is then formed into a shell structure. In a preferred embodiment, an inner spool is located within the shell structure, which acts to increase the output sound pressure level for the transducer. To increase the sound pressure level further, the inner spool preferably includes a recessed area, which defines a void between the inner conductive layer on the shell and the recessed area. The void acts to increase the characteristic output sound pressure level for the transducer. In one embodiment, the piezoelectric transducer is placed in a data entry device, such as a transmitter pen, and is used to transmit a signal from the pen to a receiver, which can be used to accurately determine the location of the pointing tip of the pen, in relation to an electronic tablet or white board.